It is known, especially in conjunction with zinc coating lines or galvanizing lines, to integrate dressing roll stands in the strip processing line to thereby emboss or otherwise impart certain surface properties to the strip and to alter in a targeted way the properties of the strip being processed. In such cases there is the danger that zinc particles, for example, which are only partly adherent to the strip can be transferred to the working and back-up rolls of a stand in the strip line. The zinc particles which remain adherent to the surface of the roll tend to be pressed into the surface with time and to imprint on subsequently rolled products, thereby introducing defects which may make a portion of the product unusable, which can require cutting out and scrapling of a portion of the product, and which can decrease productivity.
In order to reduce the risk of adhesion of particles on the rolls of a strip line and especially the rolls of a dressing mill or stand, it is known to operate the dressing stand in a wet condition. The result is a wet rolling of the strip under conditions in which particles tend to remain in the liquid and not to adhere to the dressing rolls.
Cleaning devices for such rolls in the form of brushes, fleece rollers and fleece cushions are known, these units being either as wide as the widest metal strip to be processed or being mounted to traverse along the effective length of the roll. The cleaning effect of brushes, fleece rollers and fleece cushions is, however, limited, and in many cases is unsatisfactory.
A high pressure liquid cleaning of the rolls has been proposed in which a wide mouth nozzle for each roll provides a water spray to clean the surface of the roll. With this system, the position of the cleaning nozzle cannot be varied. A nozzle system which is capable of moving along the roll is also known but this earlier system is satisfactory only for rolls of constant diameter with constant strip speeds. The wide mouth nozzle is not versatile in that especially dressing roller stands must have rolls of different roll diameter from time to time for processing different steel alloys and for different products made by the system. For example, a working roll may have a diameter of 450 mm when new and 400 mm when ground down for use with hard materials but 650 mm when new and 600 mm when ground down for softer materials. The backing rolls in this case may have diameters of 900 mm when new and 820 mm when ground down. The cleaning unit in the case of a broad slit nozzle is only properly positioned for one roll diameter and, for example if the roll is ground down, the cleaning effect is largely lost.
Similar problems arise with the rolls and roll stands used in extrusion casting and strip casting apparatus and in strip mills using continuous casting, as well as with the rolls used in rolling mill and strip processing lines.
In addition, in for example an aluminum process line problems arise with aluminum oxide which is more or less adherent to the strip surface and which can adhere to the rolls for the respective line, especially the stretching rolls of a processing line and can lead to growth of the deposit on the roll and the generation of surface defects.